Significant progress has been made on three fronts, namely the development of computer techniques for analysis and synthesis of complex sounds, the use of averaged evoked potentials in measuring various aspects of bird hearing, and experimental analysis of the vocal learning process in birds with special emphasis on innate constraints on what they will not learn, and on androgen-induced singing behavior of female birds. In the coming year further research is planned on all of these themes. Given the capability for complete synthesis of complex, biologically significant sounds, we will attempt to specify precisely which acoustic features are critical in the innate choice of acceptable models for vocal learning, using both wild and domesticated birds as subjects. Other aspects of the vocal learning process to be studied include effects of anti-estrogen on vocal learning in females, detailed analysis of developmental stages of songs, of and their significance for mature performance, including subsong, use of evoked potentials as a way of exploring hemispheric differences in avian auditory processing and in comparing relative salience of complex stimuli to young naive subjects. We are confident that, in addition to their intrinsic importance, these studies will throw light on the general question of special adaptations for the processing of biologically significant stimuli, and on certain early stages in the learning process in all organisms that display this ability, including man.